1. Field of the Invention
The present invention generally relates to methods for measuring a tension strength and, more particularly, is directed to a method of and apparatus for measuring a tension of a rectangular-shaped measured object such as a grid element constructing a color selecting electrode of a cathode ray tube.
2. Description of the Related Art
Generally, in the process for assembling the color selecting electrode of a cathode ray tube, in order to control the quality of the color selecting electrode, etc., a tension of the grid element constructing the grid assembly is measured after the grid assembly is stretched to the frame of the color selecting electrode.
In a method of measuring a tension according to the prior art, the color selecting electrode is held on a vibrator table. Then, the grid element of the color selecting electrode held on the vibrator table is vibrated by a vibrator, the frequency of which can be freely selected and a resonance point produced on the grid element in the course of the vibration of the grid element is checked visually. During this process, when a resonance point appears, for example, at the center of the grid element, the frequency of vibration is read out and the thus readout frequency is determined as the tension of the grid element. Then, by using the user terminal or the like, the read-out value (frequency) of such measured tension is input to the host computer to control the quality of the color selecting electrode or the like in the manufacturing process of a cathode ray tube.
The above conventional tension measuring method, however, relies on manual control and input in its process, such as when the resonance point is visually confirmed by an operator and when the value of the read-out frequency of the vibrator is input to the host computer through the user terminal. There are then the disadvantages that the process which relies on a human operator in the manufacturing process of the cathode ray tube cannot be simplified and that the cost of the manufacturing process of the cathode ray tube can not be reduced as is desired.